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  Frequently Asked Questions

We receive many e-mails and calls for technical support that could have been avoided by reading the instructions! While we certainly don't mind helping out our customers anytime, often you can answer your questions quickly and easily by reading the instructions thoroughly. All the basic information needed to assemble and fly your ProXX rocket motor is there.

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Dimensions - can I get a drawing showing the dimensions of ProX™ hardware to help me build my rocket?

Yes - there are downloable .pdf files in the hardware section of our products page.

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Maximum recommended liftoff weight – how do you determine this?

A minimum acceleration of 5 gees is recommended off the pad to ensure sufficient flight speed for aerodynamic stability. This ratio must be calculated with the rocket's weight in ready-to-launch condition, i.e. with everything installed including motor. That rule becomes more critical with lighter rockets equipped with heavy motor systems, like hybrids. As a general rule, you use the average thrust from the manufacturer's data or industry certification data to calculate your thrust-to-weight ratio. However, there are cases where you may wish to look more closely at the thrust-time profile of the motor early in the burn.

A good example is the Pro98® line of moonburners - this grain design results in maximum thrust at ignition, and a steady decline to zero over the course of the burn. The M520 for example has an average thrust of 520 Newtons, or about 117 pounds. Using the 5:1 rule, you might think this motor can only safely lift a rocket with a GTOW (gross takeoff weight) of 23-24 pounds. However, the M520 has an initial thrust of about 300 pounds, and the thrust does not fall below 117 pounds until several seconds into the burn. This allows this motor to safely fly rockets of higher liftoff weight. The prototype M520 was launched in a 6" rocket with a GTOW just shy of 40 pounds. Liftoff was fast and straight, and the rocket was tracked to 15,300 feet!

In this case, the performance of the motor in the first few seconds of the burn was the important issue. Thrust regression later in the burn causes no safety or stability problems.

Many standard Pro54®, Pro75® and Pro98® reloads have regressive thrust profiles as well, so in some cases you may want to look closely at the thrust-time data for those motors as well if the average thrust value is marginal with respect to proper liftoff acceleration.

If planning to launch a rocket whose thrust-to-weight ratio calculated from average thrust is below your association's or the RSO's prescribed minimum due to a regressive thrust profile, you may need to have data in hand to plead your case to the RSO.

When in doubt, keep average thrust-to-weight at 5:1 or better.

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Delay adjustment

Delay is defined from motor burnout to ejection charge firing. Not from ignition.

Pro29®, Pro38® and Pro54® rocket motors have an adjustable delay setting. Each motor is equipped with a delay element that, if left alone, will give you the delay time in the motor designation. For example, the 765J330-16A has a 16 second delay as supplied. However, using the ProDAT™ tool you can reduce this delay time.

The ProDAT™ (ProXX Delay Adjustment Tool) tool is used to reduce the delay time from the supplied setting.

Pro29® delay adjustment is performed with a Pro38® ProDAT™ tool with an additional centering ring.

The Pro38® ProDAT™ tool has four fixed delay reduction settings – that means you can choose from a total of five delay times. The delay reduction settings are minus 3, minus 5, minus 7 and minus 9 seconds – meaning you can reduce the delay time by 3,5,7 or 9 seconds. By using a delay reduction setting on the stops instead of a delay value, we were free to equip reloads with whatever maximum delay time we felt was appropriate for the size of motor.

The Pro54® ProDAT™ tool features a neat vernier adjustment, which you can set to remove any time value you choose between zero and 10 seconds from the supplied delay.

Please don’t confuse the setting on the delay tool with the actual delay time – it is the amount you are removing from the delay, not the delay time itself!

This was a common mistake early in the history of Pro38® motors when the adjustable delay concept was new to many – a few modelers stripped parachutes flying G69-12A motors with 3 second delays when they mistakenly thought they had set them to 9 seconds…oops!

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How do I remove the ejection charge if I am using electronic recovery deployment?

The ejection charge is retained by a thin plastic cap held in place by a couple of drops of adhesive. You can pry out the cap with a small screwdriver or similar tool, then tap out the ejection charge and use this powder in your deployment system.

Pro38 motors contain 1.3 grams of FFFFG black powder, Pro54 motors contain 2 grams.

You really don't need to plug the hole but you can put in a drop of epoxy or CA if you wish.

NOTE: If you have previously adjusted the delay setting with the ProDAT tool, AND have decided to use the motor without ejection charge in a different application, then you should plug the hole as the delay will burn for a few seconds after it reaches the flash hole. Some delay combustion products could vent through the flash hole and discolor or damage the motor mount tube or airframe components ahead of the motor.

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Why is there a gap between the thrust ring and the motor case on Pro38 motors?

This is normal. In production, there is some variation in the length of the propellant grains, therefore the total length of the propellant grain stack varies. The reload is designed to seat fully in the case with a gap of about .030" between the thrust ring and the casing, if the grains are exactly the design length. If the grains are a few thousandths of an inch short, then the gap will be less. If they are a little longer, the gap will be more.

Simply screw the reload into the case until it is snug but not overtight. If the gap is excessive (see instructions) disassemble the motor and check over the reload assembly. Reassemble.

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Can I use a different igniter?

Theoretically yes, but… why? You will not add any reliability with another igniter, but you certainly may lose some. The ignition system on Pro38 and Pro54 motors is exactly that - a system, and it works. Commercial electric matches are very reliable, and there is more than enough output from the pyrogen to ignite the igniter pellet contained in the top of the motor core.

Some time ago we experimented on the test stand with progressively larger and larger gaps between the electric match and the igniter pellet. The final test was successfully igniting a 6 grain Pro38 with the electric match head inserted only 1" into the motor. This is not recommended! It merely demonstrated that it was not critical to have the match head in tight contact with the igniter pellet.

If you insist on using a homemade pyrogen-dipped igniter, think about this first: we recently precisely reproduced an unusual failure of a Pro38® J class reload. The flier reported that at ignition, his motor ignited with a small flame and no thrust, and continued to burn for over a minute, with the rear end of the motor case melting and dripping into a puddle of aluminum. The rocket was destroyed. We asked the usual questions, including asking if the stock igniter was used, and if the flier made sure it was all the way up the motor core. Both answers were "yes".

This left us baffled for a while, until eventually we decided that the only way this could happen is for ignition to have occurred near the nozzle of the motor. We also knew that the stock match would not ignite the propellant directly, so how could this happen? We took a few reloads out to the test stand with some electric matches, plus a couple of pyrogen-dipped igniters.

The electric match would not ignite the propellant by itself, as we already knew. We then installed a dipped igniter a short way inside the motor, and pressed the button. Bingo! The motor burned like a road flare for about 90 seconds, and the rear of the motor case melted into a puddle of aluminum just like the failed reload. In fact, we couldn't tell the remains apart. Hmmm…

When asked again, the flier sheepishly admitted he had indeed used a homemade dipped igniter, and we figured it must have caught in the core and felt like it was properly installed, or else slipped out of place. All was forgiven, and we actually learned valuable information from the tests. The flier also said he would stick with the stock igniter from now on!

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What about the shroud on the Oxral igniters?

CTI now supplies Oxral electric matches with all Pro38® and Pro54® reloads with the exception of the G class Pro38® reloads due to the small nozzle throat. These relaods are supplied with a Daveyfire mini electric match.

These are excellent quality matches and more easily available than the units previously supplied. They come equipped with a plastic shroud around the match head.

This shroud increases ignition reliability by directing the output of the match forwards towards the ignition pellet, rather than in all directions. On all motors with a large enough nozzle throat to easily pass the igniter shroud, we previously recommended leaving it in place. However, a better method that can be used on all reloads shipped with the Oxral match is now described in the igniter instructions. The shroud is slid down out of the way. A short piece of the red plastic tube that shorts the leads together is cut off, and the match head slid into that. It serves the same function as the shroud, directing the match output forwards toward the igniter pellet, and it is far less liable to hang up in the core or throat.

On Pro75® and Pro98® reloads, the igniter is used exactly as supplied.

UPDATE: we now supply another brand of electric match igniter which does not have a shroud - however, these matches contain updated instructions for their use. There are still reloads in dealer inventory using the Oxral matches.

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Should I support the igniter in upper stage applications?

Unless you are using a very high thrust booster motor it is likely not necessary in Pro38 motors as the small core prevents the match from collapsing under typical acceleration. Many multistage flights have been made successfully with no additional support. However feel free to provide mechanical support as long as you do not overdo it. On "I" class (3G) Pro38™ and up, and any size Pro54™, you can tape the igniter to a thin wooden dowel or bamboo skewer. Use no larger than about 1/8" in diameter. Trim the dowel to the proper length so that the plastic nozzle cap can be fitted to retain the assembly.

Make sure whatever scheme you use does not cause excessive nozzle restriction, or else the sudden depressurization caused by ejecting the igniter and it's support could cause problems. Venting is good, blocking igniter gases is bad.

All Pro75® and Pro98® reloads are supplied with an igniter support dowel or tube, which should be used at all times. This support is taped alongside the electric match leads, with the end of the support resting against the bottom of the Oxral match shroud for support.

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Are Pro38® G motors model rocket or high power rocket motors?

The standard, or "Classic" propellant 1 grain G, the G69, contains 62.5 grams of propellant and otherwise meets the US definition of a model rocket motor.

The Smoky Sam 1 grain G, the G79SS, contains about 80 grams of propellant thereby exceeding the 62.5 gram threshold. Therefore it must be sold as a high power rocket motor in the US.

In Canada however, model rocket motors are defined as producing 160Ns or less of total impulse and having 125 grams or less of propellant - thus both these motors may be sold as model rocket motors in Canada.

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Why are Pro38® G motors more expensive than other G motors on the market?

The 1 grain Pro38® motors were never designed to be cost competitive with 29mm or 24mm G motors, either single use or reloadable. It is normal for the smallest motors in a particular standard diameter to be the least cost effective - this is because the consumable components such as the nozzle, forward closure, nozzle holder etc. are all fixed cost items designed for larger total impulse motors. Therefore as the motors get smaller, the cost of these components becomes progressively higher in relation to the cost of the propellant, thus the "bang for the buck" decreases.

Instead, we made them because we could - in other words we had the components on hand from the larger motors, so we decided to offer them too.

We thought for one they would be useful as low altitude test motors for 38mm HPR rockets, so we set up the delay so it could be adjusted down to 3 seconds.

Secondly, we thought they would be useful as upper stage motors to keep peak altitudes down for both test and sport flights.

Lastly, they allow some smaller 38mm models to be flown as model rockets without fussing with motor mount adapters.

So while many fliers choose other options for their G class flights, they are quite popular in the US and Canada, where the sales numbers have exceeded our expectations.

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Pro75® and Pro98® assembly and operating issues.

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What’s the deal with cross-brand compatibility?

Pro75® and Pro98® reloads kits fit both our own hardware, and RMS™ systems. The only difference is the type and number of o-rings used. All ProX™ cross-brand compatible reloads are supplied with the o-rings required for each type of hardware.


While CTI had planned all along to develop 75mm and 98mm products in the ProXX line, originally we had not planned to make them cross brand compatible but instead wanted to incorporate some fresh approaches as we did with the smaller sizes.

Before we had started any real work on the 75mm and 98mm products, a commercial customer asked us if we would develop some high thrust M class 98mm reloads that would fit their inventory of RMS™ 98/10240 hardware. Their test program was in serious jeopardy as the supply of reloads had dried up due to the disaster at Aerotech's plant. We said sure, no problem, and began work developing a custom reload for their application, the M3800. The only component that was not readily available was the nozzle; so we manufactured a mold for compatible nozzles. CTI already had in-house mold making and compression molding equipment so this was no big deal. The time from receipt of order to the first test firings was no more than about two months - our customer was in a hurry! The M3800 worked perfectly in their tests, and more were subsequently ordered. This quick-turnaround work led to a production contract for larger booster motors.

Once word spread through the rumor mill that we had made the M3800's, we got frantic requests from our Canadian dealers and customers for RMS™-compatible reloads as their large motor HPR activity had nearly ground to a halt due to lack of supply. So we also made a compatible single-throat nozzle mold for 75mm reloads and brought in a supply of liners, inhibitor etc. Several prototype 75mm and 98mm motors were flown at the ROC Lake launch in June 2002, all in RMS® hardware.

After that it quickly became apparent that there was great interest in and a need for 75 and 98mm reloads to fit flier's existing hardware. People told us they wanted alternatives, and the concept began to make more and more sense especially in light of the high cost of large hardware. Therefore we forged ahead with development of a complete line of reloads for the sport rocket market. We also designed our own hardware, incorporating our own ideas for improvement wherever possible while maintaining compatibility.

The concept of alternate brand (non-OEM) consumables or repair parts is nothing new in the world of commerce - this goes on in a vast array of industries; copiers, printers, automobile parts, ammunition to name just a handful. It therefore is somewhat inevitable that it would surface in the sport rocket market at some time. We just did it first!

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Certification status

Cross brand compatible reloads are new to HPR/MR, therefore none of the rules and regulations of the rocketry associations addressed the situation adequately when first introduced. After some discussion between the HPR associations' motor testing committees, it was decided that cross brand compatible reloads had to undergo a complete certification firing series in any hardware in which they were to be offered for use.

Currently the following reloads are certified for use in CTI ProX™ hardware and RMS™ hardware:


Classic™ propellant reloads: K510-P, L800-P, L1115-P, and M1400-P.

White Thunder™ propellant reloads: K1085-P, L1720-P and L2375-P

Red Lightning™ propellant reloads: M1810-P

Blue Streak™ propellant reloads: M1670-P

Skidmark™ propellant reloads: M1770-P


Classic™ propellant reloads: L600-P, M1060-P, M1495-P, and N2500-P.

White Thunder™ propellant reloads: M2505-P

Red Lightning™ propellant reloads: M1890-P

Vmax™ propellant reloads: L3150-P

Classic™ propellant moonburners: M520-P, M795-P, N1100-P.

Skidmark™ propellant reloads: 8088M1790-P

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How about the other way around - can RMS™ 75mm or 98mm reloads be fired in CTI hardware?

Currently no RMS™ reloads are certified for use in CTI ProX™ hardware. It is up to the reload manufacturer to supply reloads and hardware to the motor testing committees for certification firing. If Aerotech chooses to have their reloads certified for use in ProX™ hardware, that's fine but it's up to them to do so - you'll have to contact them with any questions on that subject.

Functionally, however, the answer is yes. Compatibility works both ways. We have compatible hardware in all equivalent 75mm sizes and 98mm sizes from 98/5120 up to 98/15360 case size. Several RMS™ reloads have already been flown in ProX™ hardware at Canadian launches. The only thing extra that is needed is a set of the correct o-rings for the ProX™ hardware.

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Cross reference as to which RMS™ case is to be used with which CTI™ reload

Pro75-2G = RMS75/2560

Pro75-3G = RMS75/3840

Pro75-4G = RMS75/5120

Pro75-5G = RMS75/6400

Pro75-6G = RMS75/7680

Pro98-1G = RMS98/2560

Pro98-2G = RMS98/5120

Pro98-3G = RMS98/7680

Pro98-4G = RMS98/10240

Pro98-6G = RMS98/15360

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What about the Pro-X™ No hassle warranty with cross compatible hardware?

In the event of a warranty claim where a ProX™ grain is used in a compatible motor case, we replace (on a case by case basis) the hardware with our ProX™ brand hardware, not a monetary refund or a case from the original manufacturer. The ProX™ line now has a large selection of Pro75 reloads, and a replacement case from ProX™ will not limit the flyer in terms of available colors and/or effects in any way. Further, ProX™ hardware will support an even wider variety of options in the (near) future.

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Where can I buy ProX™ motor products?

You can purchase ProX™ motor hardware, reload kits, and accessories from any of the dealers listed in our dealers section. There are dealers throughout the continental US, in Canada, and a growing network of dealers in Europe.

CTI does not sell motor products directly to consumers.

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Are ProX™ products covered by warranty?

CTI warranties its products against defects in manufacturing for a period of one year. If you have a problem with a ProX™ motor product, contact your dealer for support. Dealers usually provide replacement product from their inventory, which are then replaced by CTI to the dealer. However if this is not possible, we will arrange for replacements to be sent to your dealer. CTI can not ship reload products directly to the customer.

If you should ever have a defective reload, we will want to know all the details you can provide about the incident - manufacturing dates on the reload package, weather conditions, a description of the failure, etc. This helps us determine the cause and apply corrective measures.

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Beta testing

We receive frequent requests for beta testing of new products. Very frequent as a matter of fact… ;-)

Much as we appreciate the offer, once a new motor product has been tested at the factory and tested for certification, we have a pretty good idea whether or not it will work in your rocket… so we do not offer beta testing programs. New products are released to market once they are certified and available to the dealers. Press releases are posted on the major newsgroups and forums to alert you of new developments.

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